1. Field of the Invention
The present invention relates to an active matrix substrate and a repair method thereof, and particularly to an active matrix substrate having redundant active devices and a repair method thereof.
2. Description of Related Art
The display technology is continuously fast developing since the first black-and-white TV employing a cathode ray tube (CRT). However, the CRT display has the disadvantages of bulkiness, heaviness, high radiation, and relatively poor pixel quality. Therefore, other advanced flat display technologies have been gradually developed, among which liquid crystal displays (LCDs), having the advantages of better space efficiency, lower power consumption, lower radiation and better portability, is the most mature and popular technology. LCDs are widely used in the fields of cell phones, digital cameras, digital camcorders, personal digital assistants, notebook PCs and liquid crystal TVs.
Although the LCD technology tends to be mature, it is inevitable to produce some defects during the LCD panel manufacturing process, which may to some degree cause visual discomfort because of the LCD panel displaying images. And the production cost will be substantially raised if such an LCD panel is directly discarded. Generally, it is very difficult to achieve a zero defect ratio by merely improving manufacturing processing technologies; therefore the defect repairing technology of LCD panels is becoming more and more important. In conventional technologies, laser cutting or laser welding is often adopted for LCD panel defect repair. Taking a TFT-LCD as an example, a process of laser cutting or laser welding is usually processed after a TFT array has been manufactured. Unfortunately, because of some drawbacks of the conventional pixel structure design, not all defects may be rapidly repaired, and some of them even cannot be repaired.
FIG. 1A is a top view of a conventional TFT array substrate; FIGS. 1B and 1C are cross-sectional views of FIG. 1A respectively along with line a-b and line c-d. Referring to FIGS. 1A to 1C together, a conventional TFT array substrate 100 includes a substrate 110, a plurality of scan lines 120, a plurality of data lines 130 and a plurality of pixel units 140, wherein the scan lines 120, the data lines 130 and the pixel units 140 are all disposed on the substrate 110.
The pixel units 140 are electrically connected with the corresponding scan lines 120 and data lines 130. Each of the pixel units 140 includes a TFT 142 and a pixel electrode 144, for example, an indium tin oxide (ITO) electrode. In the prior art, the TFT 142 includes a gate electrode 142a, an amorphous silicon channel layer 142b, a source electrode 142c and a drain electrode 142d. The gate electrode 142a is connected with the scan line 120. The gate electrode 142a and the scan line 120 belongs to a first metal layer. The source electrode 142c is connected with the data line 130, and the data line 130. The source electrode 142c and the drain electrode 142d belongs to a second metal layer. The pixel electrode 144 is electrically connected with the drain electrode 142d. 
However, a defective TFT 142 may hinder the normal operation of the pixel unit 140. Such a defect corresponds to a bright dot defect on the LCD panel after the TFT substrate 100 and a color filter substrate are assembled and the liquid crystal is filled. To avoid such bright dot defects on the LCD panel, a laser repairing process is needed for repairing such bright dot defects to a dark dot. Referring to FIGS. 1A to 1C, a conventional repairing method is to weld the pixel electrode 144 with an adjacent scan line 120 via laser welding process, by which the repaired pixel unit 140 will become a dark dot.
FIG. 2A is a top view of another conventional TFT array substrate; FIGS. 2B and 2C are cross-sectional views of FIG. 2A respectively along with line a-b and line c-d. Referring to FIGS. 2A to 2C together, a conventional TFT substrate 200 includes a substrate 110, a plurality of scan lines 120, a plurality of data lines 130, a plurality of pixel units 140, a plurality of repair lines 210, a plurality of repair structures 220, wherein the scan lines 120, data lines 130, pixel units 140, repair lines 210 and repair structures 220 are disposed on the substrate 110.
The substrate 110, the scan lines 120, the data lines 130 and the pixel units 140 are the same as the foregoing disposed on the TFT array substrate 100. One terminal of the repair structure 220 is connected with the data line 120, and the other terminal of the repair structure 220 is connected with the drain electrode 142d. The repair structure 220 belongs to the second metal layer. Each repair line 210 is disposed under one of the repair structures 220 and the repair lines 210 belong to the first metal layer. A gate insulating layer 170 is disposed between the repair line 210 and the repair structure 220.
Referring to FIGS. 2A to 2C again, a defective TFT 142 may hinder the normal operation of the pixel unit 140. Such a defect corresponds to a bright dot defect on the LCD panel after the TFT substrate 100 and a color filter substrate are assembled and the liquid crystal is filled. To avoid such bright dot defects on the LCD panel, a laser cutting process is usually employed to cut the connection 150 between the gate electrode 142a and the scan line 120, and a laser welding process is then performed to weld the repair line 210 and the two terminals of the repairing structure 220. However, the repaired pixel unit is a bright dot defect or a dark dot defect. When a compensation film is attached to a large LCD panel to enhance the viewing angle, such repaired pixel units may again cause bright dot defects at some certain viewing angles due to light leakage.